Ink set for ink jet recording and ink jet recording method using the same

ABSTRACT

A cyan ink, for ink jet recording, capable of realizing good lightfastness and waterfastness and, in addition, capable of realizing a good image, especially an image having good hue, and an ink set comprising the above cyan ink in combination with a magenta ink and a yellow ink are provided. The use of a combination of C.I. Pigment Blue 60, 22, 64, or 21 with C.I. Pigment Blue 15:3 as a cyan ink enables the formation of a good image. An ink set comprising this cyan ink composition in combination with a yellow ink comprising C.I. Pigment Yellow 109 and C.I. Pigment Yellow 110 and a magenta ink comprising C.I. Pigment Red 122 or C.I. Pigment Red 209 can realize a good image.

This is a continuation of application Ser. No. 08/764,090 filed on Dec.6, 1996, now U.S. Pat. No. 5,846,306 claims the benefit thereof andincorporates the same by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to cyan and yellow ink compositions forink jet recording, an ink set comprising the ink composition, and an inkjet recording method wherein a reaction solution and an ink compositionare deposited onto a recording medium to conduct printing.

2. Background Art

Ink jet recording is a printing method wherein droplets of an inkcomposition are ejected and deposited onto a recording medium such aspaper. This method has a feature that an image with high resolution andhigh quality can be realized at a high speed by means of a relativelyinexpensive apparatus.

The ink composition used in the ink jet recording, in general, compriseswater as a main solvent and, added thereto, a colorant and a wettingagent, such as glycerin, for preventing clogging. Regarding the colorantused in the ink composition for ink jet recording, a large number ofwater-soluble dyes have been used because of their high chroma,abundance, and good solubility in water and the like.

However, dyes are poor in various properties, such as lightfastness andwaterfastness, and, hence, prints formed by using dye compositions havepoor lightfastness and waterfastness. The waterfastness of the printshas been improved for a specialty paper, for ink jet recording, havingan ink-absorptive layer, whereas it is unsatisfactory for plain papers.

On the other hand, pigments have better lightfastness and waterfastnessthan dyes. This has been led to studies on the use of pigments ascolorants in an ink composition for ink jet recording. The pigments aregenerally insoluble in water. Thus, when the use of a pigment in anaqueous ink composition is contemplated, it is necessary to disperse thepigment in water with a resin and the like as "dispersant" before thepreparation of an ink composition.

In order to stably disperse the pigment, the consideration should begiven to the type and particle diameter of the pigment, the type of theresin used, dispersing means and the like. Many dispersing systems andinks for ink jet recording have hitherto been proposed in the art. Forexample, Japanese Patent Laid-Open No. 252467/1991 proposes an inkcomposition comprising water, a styrene/maleic acid copolymer,ε-caprolactum, and a pigment. Further, Japanese Patent Laid-Open No.79680/1991 discloses an ink composition comprising an aqueous medium, astyrene/maleic acid copolymer, and a copper phthalocyanine pigment.

Studies on the use of pigments in inks for ink jet recording range fromblack inks to color inks.

The method in which a polyvalent metallic salt solution is applied on arecording medium followed by the application of an ink compositioncontaining a dye having at least one carboxyl group has been recentlyproposed, for example, in Japanese Patent Laid-Open No. 202328/1993. Theclaimed advantage of this method is that the polyvalent metal ioncombines with the dye to form an insoluble complex which can offer animage having waterfastness and high quality free from color bleeding.

Further, Japanese Patent Laid-Open No. 106735/1994 discloses the use ofa color ink containing a surfactant or a solvent for imparting apenetrating property and a salt in combination with a black ink capableof being thickened or agglomerated with the salt. The claimed advantageof this method is that a high-quality color image having a high imagedensity and free from color bleeding is realized. In this method, twoliquids, i.e. a solution containing a salt as first and an inkcomposition as second, are printed in order to yield a good image.

Although pigments have better lightfastness and waterfastness, the typeof usable pigments for this purpose is limited as compared with dyes.When pigments are actually used in the ink for ink jet recording, notonly the lightfastness and the waterfastness but hue should besufficiently studied. Properties such as lightfastness, waterfastness,and storage stability of ink compositions including a pigment for inkjet recording have been studied. However, studies on the hue of the inkcomposition including pigment and a change in hue of the ink compositionwhen used in the ink jet recording method are made unsatisfactory.

We have now found that, in a color ink jet recording method, cyan andyellow ink compositions containing specific pigments can realize goodimages. Further, we have found that a combination of the above cyan inkcomposition or yellow ink composition with other color inkcomposition(s) can provide good images. Furthermore, we have found thatthese ink compositions, when used in an ink jet recording method usingthe so-called "two liquids" wherein a reaction solution and an inkcomposition are deposited to conduct printing, can yield good images.

Accordingly, an object of the present invention is to provide cyan andyellow ink compositions, for ink jet recording, which can realize goodlightfastness and waterfastness and, in addition, good images,especially images having good hue.

Another object of the present invention is to provide an ink set, forink jet recording, which can realize good lightfastness andwaterfastness and, in addition, good images, especially images havinggood hue.

A further object of the present invention is to provide an ink jetrecording method, using two liquids, which can realize goodlightfastness and waterfastness and, in addition, good images,especially images having good hue.

According to one aspect of the present invention, there is provided acyan ink composition comprising at least one pigment represented by thefollowing formula (I): ##STR1## wherein x is an integer of 0 to 3; or, apigment represented by the following formula (II): ##STR2## or a mixtureof the pigment represented by the formula (I) with the pigmentrepresented by the formula (II).

According to another aspect of the present invention, there is provideda yellow ink composition for ink jet recording, comprising a pigmentrepresented by the following formula (III): ##STR3## wherein Y₁ to Y₈each independently represent a chlorine or hydrogen atom and Rrepresents o-phenylene or 2,6-xylyl, or C.I. Pigment Yellow 74, 138, 150or 180.

According to still another aspect of the present invention, there isprovided an ink set for ink jet recording, comprising a cyan inkcomposition, a magenta ink composition, and a yellow ink composition,wherein the cyan ink composition is the above cyan ink composition ofthe present invention.

According to a further aspect of the present invention, there isprovided an ink set for ink jet recording, comprising a cyan inkcomposition, a magenta ink composition, and a yellow ink composition,wherein the yellow ink composition is the above yellow ink compositionof the present invention.

According to a still further aspect of the present invention, there isprovided an ink set for ink jet recording, comprising a cyan inkcomposition, a magenta ink composition, and a yellow ink composition,wherein the cyan ink composition is the above cyan ink composition ofthe present invention and the yellow ink composition is the above yellowink composition of the present invention.

According to another aspect of the present invention, there is provideda ink jet recording method, comprising the step of: depositing areaction solution containing a reactant and an ink composition onto arecording medium,

wherein the ink composition is the above cyan ink composition of thepresent invention or an ink composition in the above ink set, and

the reactant breaks the state of dispersion and/or dissolution of thepigment to cause agglomeration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of the ink jet recording apparatus accordingto the present invention, wherein a recording head is providedseparately from an ink tank to feed an ink composition and a reactionsolution into a recording head through an ink tube;

FIG. 2 is an enlarged view showing the surface of nozzles for arecording head, wherein reference character 1b designates the surface ofa nozzle for a reaction solution and 1c the surface of a nozzle for anink composition;

FIG. 3 is a diagram illustrating ink jet recording using the recordinghead shown in FIG. 2, wherein numeral 31 designates a region where areaction solution has been deposited and numeral 32 a printed regionwhere an ink composition has been printed on the deposited reactionsolution;

FIG. 4 shows another embodiment of the recording head according to thepresent invention, wherein all ejection nozzles are arranged in lateraldirection;

FIG. 5 shows an embodiment of the ink jet recording apparatus accordingto the present invention, wherein a recording head is integral with anink tank; and

FIG. 6 shows another embodiment of the ink jet recording apparatusaccording to the present invention, wherein a heater is provided to heata recording medium after printing.

DETAILED DESCRIPTION OF THE INVENTION Cyan Ink Composition

The cyan ink composition for ink jet recording according to the presentinvention comprise, as a colorant, at least one pigment represented bythe formula (I), a pigment represented by the formula (II), or a mixtureof the pigment represented by the formula (I) with the pigmentrepresented by the formula (II).

Specific examples of pigments represented by the formula (I) includeC.I. Pigment Blue 60 (x=0), C.I. Pigment Blue 22 (x=1), C.I. PigmentBlue 64 (x=2), and C.I. Pigment Blue 21 (x=3).

Specific examples of pigments represented by the formula (II) includeC.I. Pigment Blue 15:3.

The cyan ink composition, according to the present invention, comprisinga mixture of the above pigments can realize good lightfastness andwaterfastness and, at the same time, a good image having good hue.Further, according to the cyan ink composition of the present invention,color shading observed in the printing obtained with an ink compositionusing only the pigment represented by the formula (II), especially C.I.Pigment Blue 15:3, can be unexpectedly eliminated by combining thepigment represented by the formula (II) with the pigment represented bythe formula (I), especially C.I. Pigment Blue 60, 22, 64, or 21. Thisalso is an advantage of the present invention.

The ratio of the content of the pigment represented by the formula (I)to the pigment represented by the formula (II) is preferably in therange of from about 1:2 to 1:10, more preferably about 1:2 to 1:8, mostpreferably about 1:2 to 1:5, in terms of the weight ratio.

The cyan ink composition according to the present invention compriseswater in addition to the pigment. The amount of the pigment added to thecyan ink composition is not limited but may be determined in such anamount range as will realize good waterfastness and lightfastness and,in addition, an image having good hue. For example, it is preferably notmore than 6% by weight.

In the present invention, preferably, the pigment is added, as a pigmentdispersion which is previously prepared by dispersing the pigment in anaqueous medium with the aid of a dispersant or a surfactant. Preferreddispersants include those commonly used in the preparation of pigmentdispersions, for example, polymeric dispersants.

According to a preferred embodiment of the present invention, the cyanink composition further comprises an organic solvent. The organicsolvent is preferably a low-boiling organic solvent. Preferred examplesof low-boiling organic solvents usable herein include methanol, ethanol,n-propyl alcohol, iso-propyl alcohol, n-butanol, sec-butanol,tert-butanol, iso-butanol, and n-pentanol. Monohydric alcohols areparticularly preferred. The low-boiling organic solvent has the effectof shortening the time taken for drying the ink.

Further, according to a preferred embodiment of the present invention,the ink composition further comprises a high-boiling organic solvent.Preferred examples of high-boiling organic solvents usable hereininclude polyhydric alcohols such as ethylene glycol, diethylene glycol,triethylene glycol, polyethylene glycol, polypropylene glycol, propyleneglycol, butylene glycol, 1,2,6-hexanetriol, thioglycol, hexylene glycol,glycerin, trimethylolethane, and trimethylolpropane; alkyl ethers ofpolyhydric alcohols, such as ethylene glycol monomethyl ether, ethyleneglycol monobutyl ether, diethylene glycol monomethyl ether, diethyleneglycol monoethyl ether, diethylene glycol monobutyl ether, triethyleneglycol monomethyl ether, and triethylene glycol monoethyl ether, andtriethylene glycol monobutyl ether; urea, 2-pyrrolidone,N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, andtriethanolamine.

The amount of the low-boiling organic solvent added is preferably in therange of from 0.5 to 10% by weight, more preferably in the range of from1.5 to 6% by weight, based on the ink composition. The amount of thehigh-boiling organic solvent added is preferably about 0.5 to 40% byweight, more preferably about 2 to 20% by weight.

According to a preferred embodiment of the present invention, the cyanink composition comprises a surfactant. Preferred examples ofsurfactants usable herein include anionic surfactants (for example,sodium dodecylbenzenesulfonate, sodium laurate and an ammonium salt of apolyoxyethylene alkyl ether sulfate); nonionic surfactants (for example,a polyoxyethylene alkyl ether, a polyoxyethylene alkyl ester, apolyoxyethylene sorbitan fatty acid ester, a polyoxyethylene alkylphenyl ether, a polyoxyethylene alkylamine, and a polyoxyethylenealkylamide). They may be used alone or as a mixture of two or more.Further, it is also possible to use acetylene glycol (OLFINE Y andSurfynol 82, 104, 440, 465, and 485 (all the above products beingmanufactured by Air Products and Chemicals Inc.).

According to a preferred embodiment of the present invention, the cyanink composition comprises a resin emulsion. The term "resin emulsion"used herein refers to an emulsion comprising water as a continuous phaseand the following resin component as a dispersed phase. Resin componentsas the dispersed phase include acrylic resin, vinyl acetate resin,styrene/butadiene resin, vinyl chloride resin, (meth)acrylate/styreneresin, butadiene resin, styrene resin, crosslinked acrylic resin,crosslinked styrene resin, benzoguanamine resin, phenolic resin,silicone resin, and epoxy resin.

According to a preferred embodiment of the present invention, the resinis a polymer having a combination of a hydrophilic segment with ahydrophobic segment. The particle diameter of the resin component is notparticularly limited so far as the resin component forms an emulsion.It, however, is preferably not more than about 150 nm, more preferablyabout 5 to 100 nm.

The above resin emulsion may be prepared by subjecting a monomer(s) forforming a contemplated resin to dispersion polymerization in wateroptionally in the presence of a surfactant. For example, an emulsion ofan acrylic resin or a styrene/acrylic resin may be prepared bysubjecting an ester of (meth)acrylic acid or alternatively an ester of(meth)acrylic acid in combination with styrene to dispersionpolymerization in water optionally in the presence of a surfactant. Ingeneral, the ratio of the resin component to the surfactant ispreferably about 10:1 to 5:1. When the amount of the surfactant usedfalls within the above range, it is possible to provide an inkcomposition which has good water resistance in the form of an image andgood penetrability. Although the surfactant is not particularly limited,preferred examples thereof include those described above.

The ratio of the resin as the component constituting the dispersed phaseto water is suitably 60 to 400 parts by weight based on 100 parts byweight of the resin with 100 to 200 parts by weight, based on 100 partsby weight of the resin, of water being preferred.

Known resin emulsions may also be used as the above resin emulsion. Forexample, resin emulsions described in Japanese Patent Publication No.1426/1987 and Japanese Patent Laid-Open Nos. 56573/1991, 79678/1991,160068/1991, and 18462/1992 as such may be used as the resin emulsion inthe present invention.

Further, commercially available resin emulsions may also be used, andexamples thereof include Microgel E-1002 and E-5002 (styrene/acrylicresin emulsion, manufactured by Nippon Paint Co., Ltd.), Voncoat 4001(acrylic resin emulsion, manufactured by Dainippon Ink and Chemicals,Inc.), Voncoat 5454 (styrene/acrylic resin emulsion, manufactured byDainippon Ink and Chemicals, Inc.), SAE-1014 (styrene/acrylic resinemulsion, manufactured by Nippon Zeon Co., Ltd.), and Saivinol SK-200(acrylic resin emulsion, manufactured by Saiden Chemical Industry Co.,Ltd).

In the cyan ink composition according to the present invention, theamount of the resin emulsion incorporated therein is preferably suchthat the amount of the resin component is in the range of from 0.1 to40% by weight, more preferably in the range of from 1 to 25% by weight.The resin emulsion has the effect of inhibiting the penetration of acoloring component into the recording medium and, further, acceleratingthe fixation on the medium. Further, some resin emulsions have anadditional effect that they form a film on the surface of an ink imageon the recording medium to improve the rubbing resistance of theresultant print.

According to a preferred embodiment of the present invention, the inkcomposition contains a thermoplastic resin in the form of a resinemulsion. In this embodiment, the thermoplastic resin has a softeningtemperature of 50 to 250° C., preferably 60 to 200° C. The term"softening temperature" used herein refers to the lowest temperatureamong the glass transition temperature of the thermoplastic resin, themelting point of the thermoplastic resin, the temperature which bringsthe viscosity of the thermoplastic resin to 10¹¹ to 10¹² poises, thepour point of the thermoplastic resin, and the minimum film formingtemperature (MFT) in the form of an emulsion of the thermoplastic resin.In the step of heating according to the method of the present invention,the recording medium is heated to at least the softening temperature ofthe thermoplastic resin.

Further, preferably, the thermoplastic resin, when heated at thesoftening or melting temperature or a higher temperature and thencooled, forms a strong film having water resistance and rubbingresistance.

Specific examples of water-insoluble thermoplastic resins include, butnot limited to, polyacrylic acid, polymethacrylic acid, an ester ofpolymethacrylic acid, polyethylacrylic acid, a styrene/butadienecopolymer, polybutadiene, an acrylonitrile/butadiene copolymer, achloroprene copolymer, a fluororesin, polyvinylidene fluoride,polyolefin resin, cellulose, a styrene/acrylic acid copolymer, astyrene/methacrylic acid copolymer, polystyrene, a styrene/acrylamidecopolymer, polyisobutyl acrylate, polyacrylonitrile, polyvinyl acetate,polyvinyl acetal, polyamide, rosin resin, polyethylene, a polycarbonate,a polyvinylidene chloride resin, a cellulosic resin, a vinyl acetateresin, an ethylene/vinyl acetate copolymer, a vinylacetate/(meth)acrylate copolymer, a vinyl chloride resin, polyurethane,and a rosin ester.

Specific examples of low-molecular weight thermoplastic resins includepolyethylene wax, montan wax, alcohol wax, synthetic oxide wax, ana-olefin/maleic anhydride copolymer, animal and vegetable waxes such ascarnauba wax, lanolin, paraffin wax, and microcrystalline wax.

According to a preferred embodiment of the present invention, the cyanink composition according to the present invention contains asaccharide. Examples of saccharides usable herein includemonosaccharides, disaccharides, oligosaccharides (includingtrisaccharides and tetrasaccharides), and other polysaccharides,preferably glucose, mannose, fructose, ribose, xylose, arabinose,galactose, aldonic acid, glucitol, sorbitol, maltose, cellobiose,lactose, sucrose, trehalose, and maltotriose. The term "polysaccharide"used herein refers to saccharides, in a broad sense, includingsubstances which widely exist in the natural world, such as alginicacid, α-cyclodextrin, and cellulose.

Derivatives of these saccharides include reducing sugars of the abovesaccharides (for example, sugar alcohols represented by the generalformula HOCH₂ (CHOH)_(n) CH₂ OH wherein n is an integer of 2 to 5),oxidized sugars (for example, aldonic acid and uronic acid), amino acid,and thiosugars. Sugar alcohols are particularly preferred, and specificexamples thereof include maltitol and sorbitol.

The content of the above saccharide is suitably in the range of from 0.1to 40% by weight, preferably 0.5 to 30% by weight, based on the ink.

Further, if necessary, pH adjustors, preservatives, antimolds and thelike may be added.

Yellow Ink Composition

The yellow ink composition according to the present invention comprises,as a colorant, a pigment represented by the formula (III) or C.I.Pigment Yellow 74, 138, 150 or 180 as defined above.

According to a preferred embodiment of the present invention, the yellowink composition comprises, as a pigment represented by the formula(III), C.I. Pigment Yellow 109 which is a pigment represented by theformula (III) wherein Y₁ to Y₈ represent a chlorine atom and Rrepresents 2,6-xylyl and C.I. Pigment Yellow 110 which is a pigmentrepresented by the formula (III) wherein Y₁ to Y₈ represent a chlorineatom and R represents o-phenylene. According to a further preferredembodiment of the present invention, the weight ratio of C.I. PigmentYellow 109 to the content of C.I. Pigment yellow 110 is preferably inthe range of from 60:40 to 99:1. The use of these two pigments incombination can realize good hue and color density.

The yellow ink composition according to the present invention compriseswater in addition to the above pigment. The amount of the pigment addedto the yellow ink composition is not limited but may be determined insuch an amount range as will realize good waterfastness andlightfastness and, in addition, an image having good hue. For example,it is preferably not more than 6% by weight.

As the cyan ink composition, the yellow pigment may preferably be addedto the ink composition as a pigment dispersion which is previouslyprepared by dispersing the pigment in an aqueous medium with the aid ofa dispersant or a surfactant. Preferred dispersants include thosecommonly used in the preparation of pigment dispersions, for example,polymeric dispersants.

Further, as the cyan ink composition, the yellow ink compositionaccording to the present invention preferably further comprisesadditives such as an organic solvent, a surfactant, a resin emulsion, asaccharose, a pH adjustor, a preservative, and an antimold. Specificexamples thereof and the amount thereof added may be the same as thosedescribed above in connection with the cyan ink composition.

Ink Set

The ink set according to the present invention basically comprises acyan ink composition, a magenta ink composition, and a yellow inkcomposition, the cyan ink composition being the above cyan inkcomposition of the present invention.

The ink set according to another aspect of the present inventionbasically comprises a cyan ink composition, a magenta ink composition,and a yellow ink composition, the yellow ink composition being the aboveyellow ink composition of the present invention.

The ink set according to a further aspect of the present inventionbasically comprises a cyan ink composition, a magenta ink composition,and a yellow ink composition, the cyan ink composition being the abovecyan ink composition of the present invention, the yellow inkcomposition being the above yellow ink composition of the presentinvention.

The ink set according to the present invention can realize goodlightfastness and waterfastness and, in addition, an image having goodhue.

In the ink set according to the present invention, the magenta inkcomposition is not particularly limited so far as it is not detrimentalto the above good properties of the cyan ink composition and the yellowink composition. However, a magenta ink composition comprising thefollowing pigment as a colorant is preferred.

Specifically, a preferred magenta ink composition comprises, as acolorant, a pigment represented by the following formula (IV): ##STR4##wherein X₁ to X₁₀ each independently represent a hydrogen or chlorineatom or a methyl group.

Specific examples of pigments represented by the formula (IV) includeC.I. Pigment Red 122 which is a pigment represented by the formula (IV)wherein X₂ and X₇ represent a methyl group and the other substituentsX₁, X₂ to X₆, and X₈ to X₁₀ represent a hydrogen atom and C.I. PigmentRed 209 which is a pigment represented by the formula (IV) wherein X₃and X₈ represent a chlorine atom and the other substituents X₁, X₂, X₄to X₇, and X₉ and X₁₀ represent a hydrogen atom.

The ink set using the above magenta ink composition can realize a goodcolor image.

According to a preferred embodiment of the present invention, there isprovided an ink set including the combination of the magenta inkcomposition containing C.I. Pigment Red 122 or 209 and the cyan inkcomposition containing C.I. Pigment Blue 60 as a pigment represented bythe formula (I) or C.I. Pigment Blue 15:3 as a pigment represented bythe formula (II).

According to a preferred embodiment of the present invention, theconcentration of the magenta pigment in the magenta ink composition andthe concentration of the yellow pigment in the yellow ink compositioneach are higher than the concentration of the cyan pigment in the cyanink composition. More preferably, the pigment concentration is not morethan 6% by weight for all the ink compositions and the ratio of thepigment concentration (% by weight) of the cyan ink composition to thepigment concentration (% by weight) of the magenta ink composition tothe pigment concentration (% by weight) of the yellow ink composition is1:1 to 2:1 to 3. According to this embodiment, an image having furtherimproved hue can be realized.

The magenta ink composition constituting the ink set according to thepresent invention comprises at least water in addition to the abovepigment. The amount of the pigment added to the ink composition is notlimited but may be determined in such an amount range as will realizegood waterfastness and lightfastness and, in addition, an image havinggood hue. For example, it is preferably not more than 6% by weight.

As with the cyan ink composition, in the magenta ink compositionconstituting the ink set according to the present invention, preferably,the pigment is added, as a pigment dispersion prepared by dispersing thepigment in an aqueous medium with the aid of a dispersant or asurfactant, to the ink composition. Preferred dispersants include thosecommonly used in the preparation of pigment dispersions, for example,polymeric dispersants.

Further, as with the cyan ink composition, the magenta ink compositionconstituting the ink set according to the present invention preferablyfurther comprises additives such as an organic solvent, a surfactant, aresin emulsion, a saccharose, a pH adjustor, a preservative, and anantimold. Specific examples thereof and the amount thereof added may bethe same as those described above in connection with the cyan inkcomposition.

Ink Jet Recording Method Using Two Liquids

The cyan ink composition and the ink set according to the presentinvention may form an image by ink jet recording. Combination of thecyan ink composition or the ink set according to the present inventionwith the recording method using "two liquids" can offer a better image.In particular, good color development can be offered even on plainpapers. Further, as compared with the sole use of the ink composition orthe ink set, the combination of the ink composition for the ink set withthe ink jet recording method using two liquids can offer improvedlightfastness of the printed image.

The ink jet recording method according to the present invention involvesthe step of depositing a reaction solution containing a reactant and thecyan ink composition or an ink composition in the ink set of the presentinvention onto a recording medium. The term "reactant" used hereinrefers to a material which is able to break the state of dispersionand/or dissolution of the pigment and can agglomerate the pigment.

In the recording method using two liquids according to the presentinvention, a good print can be realized by contact of the reactionsolution with the ink composition. Specifically, upon contact of thereaction solution with the ink composition, the reactant contained inthe reaction solution breaks the state of dispersion of the pigment andother components in the ink composition, leading to agglomeration of thepigment and the other components. The agglomerate is considered todeposit onto the recording medium, realizing a print having high colordensity and no significant bleeding or feathering and unevenness.Further, advantageously, in the case of a color image, unevencolor-to-color intermixing in the region of boundary between differentcolors, that is, color bleeding, can be effectively prevented.

In the method of the present invention, the reaction solution is broughtinto contact with the ink composition. The step of ejecting droplets ofthe ink composition onto the recording medium to record an image may beconducted either before or after the deposition of the reaction solutiononto the recording medium. With the practice of the step of recordingafter the deposition of the reaction solution may be preferred.

The reaction solution may be selectively deposited on only the areaswhere the ink composition is deposited, or alternatively may bedeposited on the whole area of the recording medium. The former methodcan minimize the consumption of the reaction solution and, hence, iscost-effective. In the former method, however, both the reactionsolution and the ink composition should be deposited onto a contemplatedposition with certain accuracy. On the other hand, in the latter method,the requirement for the accuracy on the position of the deposition ofthe reaction solution and the ink composition is reduced as comparedwith the former method. However, the latter method is disadvantageous inthat a large amount of the reaction solution is deposited onto the wholearea of the recording medium, causing paper, when used as the recordingmedium, to be likely to curl upon drying. Therefore, which method isused may be determined by taking into consideration a combination of theink composition with the reaction solution. In the former method, thereaction solution may be deposited by the ink jet recording method.

The reaction solution used in the present invention comprises a reactantwhich can break the state of dispersion of the colorant and the othercomponents in the ink composition and can agglomerate the colorantcomponent and the other components.

Examples of the reaction solution usable in the present inventioninclude, as the reactant, a polyvalent metal salt, a polyamine, apolyamine derivative.

Preferred examples of the polyvalent metal salt include the salt whichis constituted by divalent or higher polyvalent metallic ions and anionsbonded to the polyvalent metallic ions and is soluble in water. Specificexamples of polyvalent metallic ions include divalent metallic ions,such as Ca²⁺, Cu²⁺, Ni²⁺, Mg²⁺, Zn²⁺, and Ba²⁺, trivalent metallic ions,such as Al³⁺, Fe³⁺, and Cr³⁺. Anions include Cl⁻, NO₃ ⁻, I⁻, Br⁻, ClO₃⁻, and CH₃ COO⁻.

In particular, a metal salt constituted by Ca²⁺ or Mg²⁺ providesfavorable results in terms of pH of the reaction solution and thequality of prints.

The concentration of the polyvalent metal salt in the reaction solutionis not limited but may be determined so as to attain the effect ofproviding a good print quality and preventing clogging. It, however, ispreferably about 0.1 to 40% by weight, more preferably about 5 to 25% byweight.

According to a preferred embodiment of the present invention, thepolyvalent metal salt contained in the reaction solution is constitutedby divalent or higher polyvalent metallic ions and nitrate ions orcarboxylate ions bonded to the polyvalent metallic ions and is solublein water.

The carboxylate ions are preferably derived from a carboxylic acidselected from the group consisting of a saturated aliphaticmonocarboxylic acid having 1 to 6 carbon atoms and a carbocyclicmonocarboxylic acid having 7 to 11 carbon atoms. Preferred examples ofthe saturated aliphatic monocarboxylic acid having 1 to 6 carbon atomsinclude formic acid, acetic acid, propionic acid, butyric acid,isobutyric acid, valeric acid, isovaleric acid, pivalic acid, andhexanoic acid. Among them, formic acid and acetic acid are particularlypreferred.

A hydrogen atom(s) on the saturated aliphatic hydrocarbon residue in themonocarboxylic acid may be substituted by a hydroxyl group. Preferredexamples of such carboxylic acids include lactic acid.

Preferred examples of the carbocyclic monocarboxylic acid having 6 to 10carbon atoms include benzoic acid and naphthoic acid with benzoic acidbeing more preferred.

The polyallylamine and polyallylamine derivative usable in the reactionsolution are cationic polymers which are soluble in water and can bepositively charged in water. Such polymers include, for example, thoserepresented by the following formulae (a), (b), and (c). ##STR5##wherein X⁻ represents a chloride, bromide, iodide, nitrate, phosphate,sulfate, or acetate ion.

In addition, a copolymer of an allylamine with a diallylamine and acopolymer of diallylmethylammmonium chloride with sulfur dioxide mayalso be used.

The content of the polyallylamine and the polyallylamine derivative ispreferably 0.5 to 10% by weight based on the reaction solution.

According to a preferred embodiment of the present invention, thereaction solution may contain a wetting agent comprising a high-boilingorganic solvent. The high-boiling organic solvent can prevent thereaction solution from being evaporated, preventing clogging of arecording head. Preferred examples of high-boiling organic solventsinclude polyhydric alcohols such as ethylene glycol, diethylene glycol,triethylene glycol, polyethylene glycol, polypropylene glycol, propyleneglycol, butylene glycol, 1,2,6-hexanetriol, thioglycol, hexylene glycol,glycerin, trimethylolethane, and trimethylolpropane; alkyl ethers ofpolyhydric alcohols, such as ethylene glycol monoethyl ether, ethyleneglycol monobutyl ether, diethylene glycol monomethyl ether, diethyleneglycol monoethyl ether, diethylene glycol monobutyl ether, triethyleneglycol monomethyl ether, and triethylene glycol monoethyl ether, andtriethylene glycol monobutyl ether; urea, 2-pyrrolidone,N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, andtriethanolamine.

Although the amount of the high-boiling organic solvent added is notparticularly limited, it is preferably about 0.5 to 40% by weight, morepreferably about 2 to 20% by weight.

According to a preferred embodiment of the present invention, thereaction solution comprises a low-boiling organic solvent. Preferredexamples of low-boiling organic solvents usable herein include methanol,ethanol, n-propyl alcohol, iso-propyl alcohol, n-butanol, sec-butanol,tert-butanol, iso-butanol, and n-pentanol. Monohydric alcohols areparticularly preferred. The low-boiling organic solvent has the effectof shortening the time taken for drying the ink composition. The amountof the low-boiling organic solvent added is preferably in the range offrom 0.5 to 10% by weight, more preferably in the range of from 1.5 to6% by weight.

According to a preferred embodiment of the present invention, thereaction solution comprises a penetrating agent. Penetrating agentsusable herein include various surfactants such as anionic, cationic, andamphoteric surfactants; alcohols such as methanol, ethanol, andiso-propyl alcohol; and lower alkyl ethers of polyhydric alcohols, suchas ethylene glycol monomethyl ether, diethylene glycol monoethyl ether,diethylene glycol monobutyl ether, triethylene glycol monobutyl ether,propylene glycol monobutyl ether, and dipropylene glycol monobutylether.

An ink jet recording apparatus for practicing the ink jet recordingmethod according to the present invention will now be described withreference to the accompanying drawings.

FIG. 1 is a diagram showing an embodiment of an ink jet recordingapparatus. In this embodiment, an ink composition and a reactionsolution are accommodated in a tank and fed into a recording headthrough an ink tube. Specifically, a recording head 1 is communicatedwith an ink tank 2 through an ink tube 3. The interior of the ink tank 2is partitioned, and a chamber for an ink composition, optionally aplurality of chambers respectively for a plurality of color inkcompositions, and a chamber for a reaction solution are provided.

The recording head 1 is moved along a carriage 4 by means of a timingbelt 6 driven by a motor 5. On the other hand, paper 7 as a recordingmedium is placed by a platen 8 and a guide 9 at a position facing therecording head 1. In this embodiment, a cap 10 is provided. A suctionpump 11 is connected to the cap 10 in order to conduct the so-called"cleaning operation." The ink composition sucked by the pump 11 isresorvoired in a waste ink tank 13 through a tube 12.

FIG. 2 is an enlarged view showing the surface of nozzles for therecording head 1. In the drawing, the surface of a nozzle for a reactionsolution is indicated by 1b, and a nozzle 21 for ejecting the reactionsolution is provided in the longitudinal direction. On the other hand,the surface of nozzles for the ink composition is indicated by 1c and ayellow ink composition, a magenta ink composition, a cyan inkcomposition, and a black ink composition are ejected respectivelythrough nozzles 22, 23, 24 and 25.

Further, an ink jet recording method using the recording head shown inFIG. 2 will be described with reference to FIG. 3. The recording head 1is moved in the direction indicated by an arrow A, during which time thereaction solution is ejected through the nozzle 21 to (FIG. 2) form areaction solution-deposited region 31 in a band form on the recordingmedium 7. Subsequently, the recording medium 7 is transferred by apredetermined extent in the direction indicated by an arrow B., duringwhich time the recording head 1 is moved the direction opposite to thatindicated by the arrow A and returned to the left end of the recordingmedium 7, and the recording head conduct printing using the inkcomposition on the reaction solution-deposited region 31, therebyforming a print region 32.

Further, as shown in FIG. 4, in the recording head 1, it is alsopossible to arrange all nozzles in the lateral direction to construct anozzle assembly. In the drawing, ejection nozzles for a reactionsolution are denoted by 41a and 41b, and a yellow ink composition, amagenta ink composition, a cyan ink composition, and a black inkcomposition are ejected respectively through nozzles 42, 43, 44 and 45.In the recording head according to this embodiment, the recording head1, when reciprocated on the carriage, can conduct printing in bothdirections. Therefore, in this case, printing at a higher speed isexpected as compared with the case where the recording head shown inFIG. 2 is used.

Further, when the reaction solution and the ink composition arepreferably adjusted so as to fall within the surface tension rangesdescribed above, a high-quality print can be more stably providedregardless of the order of deposition of the reaction solution and theink composition. In this case, even the provision of a single ejectionnozzle suffices for satisfactory results. For example, in the drawing,the nozzle 41b may be omitted. This can contribute to a furtherreduction in size of the head and a further increase in printing speed.

In the ink jet recording apparatus, the supplement of the inkcomposition may be carried out by replacing an ink tank in a cartridgeform. The ink tank may be integral with the recording head. A preferredembodiment of an ink jet recording apparatus using such an ink tank isshown in FIG. 5. In the drawing, the same members as used in theapparatus shown in FIG. 1 have the same reference numerals. In theembodiment shown in FIG. 5, recording heads 1a and 1b are integralrespectively with ink tanks 2a and 2b. An ink composition and a reactionsolution are ejected respectively through the recording heads 1a and 1b.Basically, printing may be conducted in the same manner as describedabove in connection with the apparatus shown in FIG. 1. Further, in thisembodiment, the recording head 1a is moved together with the ink tank 2aon a carriage 4, while the recording head 1a is moved together with theink tank 2b on the carriage 4.

A preferred embodiment of an ink jet recording apparatus wherein aheater for heating a printed recording medium is further provided isshown in FIG. 6. The embodiment shown in FIG. 6 is the same as theembodiment shown in FIG. 1, except that a heater 14 is additionallyprovided. The heater 14 may be of a contact type wherein, in heating therecording medium, it is brought into contact with the recording medium.Alternatively, the heating means may be of a non-contact type where therecording medium is heated by applying infrared rays or the like orblowing hot air to the recording medium.

EXAMPLES

The present invention will be described in more detail with reference tothe following examples, though it is not limited to these examples only.

A reaction solution and ink compositions were prepared according to thefollowing formulations.

    ______________________________________                                        Reaction solution                                                             ______________________________________                                        Magnesium acetate tetrahydrate                                                                         25 wt %                                              Triethylene glycol monobutyl ether                                                                     5 wt %                                               Glycerin                 20 wt %                                              Ion-exchanged water      Balance                                              Example 1                                                                     Pigment                                                                       Cyan ink: C.I. Pigment Blue 15:3                                                                       1 wt %                                               C.I. Pigment Blue 60     0.5 wt %                                             Magenta Ink: C.I. Pigment Red 122                                                                      2 wt %                                               Yellow ink: C.I. Pigment Yellow 109                                                                    2.4 wt %                                             C.I. Pigment Yellow 110  1.8 wt %                                             Liquid medium                                                                 Styrene/acrylic copolymer                                                                              1.5 wt %                                             ammonium salt                                                                 (molecular weight 7000, resin                                                 component 38%; dispersant)                                                    Grandoll PP-1000         7 wt %                                               (styrene/acrylic resin emulsion,                                              resin component 45%, manufactured by                                          Dainippon Ink and Chemicals, Inc.)                                            Maltitol                 7 wt %                                               Glycerin                 10 wt %                                              2-Pyrrolidone            2 wt %                                               Ion-exchanged water      Balance                                              Example 2                                                                     Pigment                                                                       Cyan ink: C.I. Pigment Blue 15:3                                                                       2.5 wt %                                             C.I. Pigment Blue 60     0.25 wt %                                            Magenta Ink: C.I. Pigment Red 209                                                                      3 wt %                                               Yellow ink: C.I. Pigment Yellow 137                                                                    1.5 wt %                                             C.I. Pigment Yellow 173  2.5 wt %                                             Liquid medium                                                                 Styrene/acrylic copolymer                                                                              1.5 wt %                                             ammonium salt                                                                 (molecular weight 7000, resin                                                 component 38%; dispersant)                                                    Voncoat 5454             5 wt %                                               (styrene/acrylic resin emulsion,                                              resin component 45%,                                                          manufactured by Dainippon Ink                                                 and Chemicals, Inc.)                                                          Sucrose                  10 wt %                                              Glycerin                 10 wt %                                              2-Pyrrolidone            2 wt %                                               Ion-exchanged water      Balance                                              Example 3                                                                     Pigment                                                                       Cyan ink: C.I. Pigment Blue 15:3                                                                       2 wt %                                               Magenta Ink: C.I. Pigment Red 122                                                                      2 wt %                                               Yellow ink: C.I. Pigment Yellow 109                                                                    2.4 wt %                                             C.I. Pigment Yellow 110  1.6 wt %                                             Liquid medium                                                                 Styrene/acrylic copolymer                                                                              1.5 wt %                                             ammonium salt                                                                 (molecular weight 7000, resin                                                 component 38%; dispersant)                                                    Grandoll PP-1000         7 wt %                                               (styrene/acrylic resin emulsion,                                              resin component 45%,                                                          manufactured by Dainippon Ink                                                 and Chemicals, Inc.)                                                          Maltitol                 7 wt %                                               Glycerin                 10 wt %                                              2-Pyrrolidone            2 wt %                                               Ion-exchanged water      Balance                                              Example 4                                                                     Pigment                                                                       Cyan ink: C.I. Pigment Blue 15:3                                                                       2 wt %                                               Magenta Ink: C.I. Pigment Red 122                                                                      4 wt %                                               Yellow ink: C.I. Pigment Yellow 109                                                                    5.94 wt %                                            C.I. Pigment Yellow 110  0.06 wt %                                            Liquid medium                                                                 Styrene/acrylic copolymer                                                                              1.5 wt %                                             ammonium salt                                                                 (molecular weight 7000, resin                                                 component 38%; dispersant)                                                    Voncoat 5454             5 wt %                                               (styrene/acrylic resin emulsion,                                              resin component 45%,                                                          manufactured by Dainippon Ink                                                 and Chemicals, Inc.)                                                          Sucrose                  10 wt %                                              Glycerin                 10 wt %                                              2-Pyrrolidone            2 wt %                                               Ion-exchanged water      Balance                                              Example 5                                                                     Pigment                                                                       Cyan ink: C.I. Pigment Blue 15:3                                                                       2 wt %                                               Magenta Ink: C.I. Pigment Red 122                                                                      3 wt %                                               Yellow ink: C.I. Pigment Yellow 138                                                                    3 wt %                                               Liquid medium                                                                 Styrene/acrylic copolymer                                                                              1.5 wt %                                             ammonium salt                                                                 (molecular weight 7000, resin                                                 component 38%; dispersant)                                                    Voncoat 5454             5 wt %                                               (styrene/acrylic resin emulsion,                                              resin component 45%,                                                          manufactured by Dainippon Ink                                                 and Chemicals, Inc.)                                                          Sucrose                  10 wt %                                              Glycerin                 10 wt %                                              2-Pyrrolidone            2 wt %                                               Ion-exchanged water      Balance                                              Example 6                                                                     Pigment                                                                       Cyan ink: C.I. Pigment Blue 15:3                                                                       1.5 wt %                                             C.I. Pigment Blue 60     0.5 wt %                                             Magenta Ink: C.I. Pigment Red 209                                                                      3 wt %                                               Yellow ink: C.I. Pigment Yellow 150                                                                    4 wt %                                               Liquid medium                                                                 Styrene/acrylic copolymer                                                                              1.5 wt %                                             ammonium salt                                                                 (molecular weight 7000, resin                                                 component 38%; dispersant)                                                    Grandoll PP-1000         5 wt %                                               (styrene/acrylic resin emulsion,                                              resin component 45%,                                                          manufactured by Dainippon Ink                                                 and Chemicals, Inc.)                                                          Sucrose                  10 wt %                                              Glycerin                 10 wt %                                              2-Pyrrolidone            2 wt %                                               Ion-exchanged water      Balance                                              Example 7                                                                     Pigment                                                                       Cyan ink: C.I. Pigment Blue 15:3                                                                       2 wt %                                               Magenta Ink: C.I. Pigment Red 122                                                                      4 wt %                                               Yellow ink: C.I. Pigment Yellow 180                                                                    4 wt %                                               Liquid medium                                                                 Styrene/acrylic copolymer                                                                              1.5 wt %                                             ammonium salt                                                                 (molecular weight 7000, resin                                                 component 38%; dispersant)                                                    Grandoll PP-1000         5 wt %                                               (styrene/acrylic resin emulsion,                                              resin component 45%,                                                          manufactured by Dainippon Ink                                                 and Chemicals, Inc.)                                                          Maltitol                 7 wt %                                               Glycerin                 10 wt %                                              2-Pyrrolidone            2 wt %                                               Ion-exchanged water      Balance                                              Example 8                                                                     Pigment                                                                       Cyan ink: C.I. Pigment Blue 15:3                                                                       1.5 wt %                                             C.I. Pigment Blue 60     0.5 wt %                                             Magenta Ink: C.I. Pigment Red 209                                                                      4 wt %                                               Yellow ink: C.I. Pigment Yellow 74                                                                     3 wt %                                               Liquid medium                                                                 Styrene/acrylic copolymer                                                                              1.5 wt %                                             ammonium salt                                                                 (molecular weight 7000, resin                                                 component 38%; dispersant)                                                    Voncoat 5454             5 wt %                                               (styrene/acrylic resin emulsion,                                              resin component 45%,                                                          manufactured by Dainippon Ink                                                 and Chemicals, Inc.)                                                          Sucrose                  5 wt %                                               Glycerin                 15 wt %                                              2-Pyrrolidone            2 wt %                                               Ion-exchanged water      Balance                                              Comparative Example 1                                                         Pigment                                                                       Cyan ink: C.I. Pigment Blue 18                                                                         2 wt %                                               Magenta Ink: C.I. Pigment Red 67                                                                       3 wt %                                               Yellow ink: C.I. Pigment Yellow 13                                                                     2 wt %                                               Liquid medium                                                                 Styrene/acrylic copolymer                                                                              1.5 wt %                                             ammonium salt                                                                 (molecular weight 7000, resin                                                 component 38%; dispersant)                                                    Voncoat 5454             5 wt %                                               (styrene/acrylic resin emulsion,                                              resin component 45%,                                                          manufactured by Dainippon Ink                                                 and Chemicals, Inc.)                                                          Maltitol                 7 wt %                                               Glycerin                 10 wt %                                              2-Pyrrolidone            2 wt %                                               Ion-exchanged water      Balance                                              ______________________________________                                    

Evaluation 1: Composite Black

The ink sets prepared in Examples 1 and 2 and Comparative Example 1 wereused to evaluate the hue of composite black.

A solid image of composite black formed by printing yellow, magenta, andcyan inks, prepared in Examples 1 and 2 and Comparative Example 1, in aratio of the yellow ink to the magenta ink to the cyan ink of 1:1:1 interms of the amount of these inks used was formed on a specialty paperfor ink jet recording (specialty paper for MJ-700V2C) by means of an inkjet printer MJ-700V2C (manufactured by Seiko Epson Corporation).

The value of a*b* was measured for the solid image. In the evaluation ofthe hue, for the solid image, the L*a*b* color system of the colordifference indication method specified in CIE was measured with MacbethCE-7000 spectrophotometer manufactured by Macbeth. In the evaluation ofthe composite black, the measured a*b* values were plotted on an a*b*coordinate, and the composite black was evaluated in terms of theabsolute value of the distance from a*=0, b*=0 (achromatic color)determined by the following equation:

    Δa*b*=(a.sup.*2 +b.sup.*2).sup.1/2

The evaluation criteria are as follows.

Δa*b*≦10 . . . good (◯)

Δa*b*>10 . . . failure (X)

Evaluation 2: Color Development on Plain Paper

An ink jet printer MJ-700V2C was used in this evaluation test. Thereaction solution was printed (100% duty) on the following recordingpapers, and inks were then printed. For comparison, inks were printed onthe recording papers with no reaction solution printed thereon.

The color development of these prints were evaluated according to thefollowing criteria.

Papers for evaluation

(1) Xerox P (Xerox Corp.)

(2) Ricopy 6200 (Ricoh Co. Ltd.)

(3) Xerox 4024 3R 721 (Xerox Corp.)

(4) Neenah Bond (Kimberly-Clark)

(5) Xerox R (Xerox Corp.)

(6) Yamayuri (Honshu Paper Co., Ltd.)

The OD value of the prints thus obtained was measured with a Macbethdensitometer (manufactured by Macbeth). The results were evaluated asfollows.

Vivid color development for all the plain papers for evaluation and anOD value of not less than 0.9 . . . ◯

Obscured color development for at least one of the papers for evaluationand an OD value of not less than 0.9 . . .

Obscured color development for at least one of the papers for evaluationand an OD value of less than 0.9 . . . X

Evaluation 3: Lightfastness

For the inks of Examples 1 and 2 and Comparative Example 1, a solid(100% duty) image (3 cm×3 cm) of each of the yellow, magenta, and cyanwas formed on a specialty paper (specialty paper for ink jet recording,manufactured by Seiko Epson Corporation) previously coated with thereaction solution, and the printed images were exposed to light (xenonFade-O-meter) for 400 hr.

In the evaluation of the hue, regarding the initial color and the colorafter the initiation of the lightfastness test for the formed solidimage, the L*a*b* color system of the color difference indication methodspecified in CIE was measured with Macbeth CE-7000 spectrophotometermanufactured by Macbeth, and the color difference between the initialcolor of the printed image and the color of the printed image after theevaluation of the lightfastness was determined based on the measuredL*a*b* values, and the lightfastness of the ink was evaluated in termsof hue change according to the following criteria.

For comparison, a test and evaluation for lightfastness were performedin the same manner as described just above, except that the paper usedwas a specialty paper, for ink jet recording, not coated with thereaction solution.

The color difference is defined by the following equation.

    Color difference: ΔE*ab=[(ΔL*).sup.2 +(Δa*).sup.2 +(Δb*).sup.2 ].sup.1/2

Evaluation criteria are as follows.

ΔE*ab≦5 for all of yellow, magenta, and cyan inks . . . excellent ()

5<ΔE*ab≦10 for all of yellow, magenta, and cyan inks . . . good (◯)

ΔE*ab>10 for at least one of the three colors . . . failure (X)

The evaluation results are summarized in the following table.

                  TABLE 1                                                         ______________________________________                                                         Evaluation 2  Evaluation 3                                          Evalua-   Reaction solution                                                                           Reaction solution                              Example                                                                              tion 1    Used   Not Used Used Not Used                                ______________________________________                                        1      ◯                                                                           ◯                                                                        Δ  ⊚                                                                   ◯                           2      ◯                                                                           ◯                                                                        Δ  ⊚                                                                   ◯                           3      ◯                                                                           ◯                                                                        Δ  ⊚                                                                   ◯                           4      ◯                                                                           ◯                                                                        Δ  ⊚                                                                   ◯                           5      ◯                                                                           ◯                                                                        Δ  ⊚                                                                   ◯                           6      ◯                                                                           ◯                                                                        Δ  ⊚                                                                   ◯                           7      ◯                                                                           ◯                                                                        Δ  ⊚                                                                   ◯                           8      ◯                                                                           ◯                                                                        Δ  ⊚                                                                   ◯                           Compara-                                                                             X         ◯                                                                        X        X    X                                       tive                                                                          Example                                                                       ______________________________________                                    

What is claimed is:
 1. An ink set for inkjet recording, comprising acyan ink composition, a magenta ink composition, and a yellow inkcomposition,wherein the cyan ink composition comprises a pigmentrepresented by the following formula (I): ##STR6## wherein x is aninteger of 0 to 3; or, a pigment represented by the following formula(II): ##STR7## or, a mixture of the pignemt represented by formula (I)with the pigment represented by formula (II); wherein the yellow inkcomposition comprises at least one pigment represented by the followingformula (III): ##STR8## wherein Y₁ to Y₈ each independently represent achlorine or hydrogen atom and R represents o-phenylene or 2,6-xylyl, orC.I. Pigment Yellow 74, 138, 150 or 180, and wherein the magenta inkcomposition comprises a pigment represented by the following formula(IV): ##STR9## wherein X₁ to X₁₀ each independently represent a hydrogenor chlorine atom or a methyl group, wherein the respective pigments ofsaid cyan, magenta and yellow ink compositions are present in therespective ink compositions in respective pigment concentrations that donot exceed 6% by weight and wherein a weight ratio of the pigmentconcentration of the cyan ink composition to the pigment concentrationof the magenta ink composition to the pigment concentration of theyellow ink composition is 1:1 to 2:1 to
 3. 2. The ink set according toclaim 1 wherein the pigment represented by the formula (I) is C.I.Pigment Blue 60, 22, 64, or
 21. 3. The ink set according to claim 1wherein the pigment represented by the formula (II) is C.I. Pigment Blue15:3.
 4. The ink set according to claim 1 wherein the weight ratio ofthe pigment represented by the formula (I) to the pigment represented bythe formula (II) is 1:2 to 1:10.
 5. The ink set according to claim 1,wherein the cyan, yellow and magenta ink compositions each furthercomprises a resin emulsion.
 6. The ink set according to claim 1 whereinthe pigment represented by the formula (II) is C.I. Pigment Yellow 109and C.I. Pigment Yellow
 110. 7. The ink set according to claim 6 whereinthe weight ratio of C.I. Pigment Yellow 109 to C.I. Pigment Yellow 110is 60:40 to 99:1.
 8. The ink set according to claim 1 wherein thepigment represented by the formula (IV) is C.I. Pigment Red 122 or C.I.Pigment Red
 209. 9. The ink set according to claim 1 wherein theconcentration of the magenta pigment in the magenta ink composition andthe concentration of the yellow pigment in the yellow ink compositioneach are higher than the concentration of the cyan pigment in the cyanink composition.